The instant invention pertains to semiconductor device fabrication and processing and more specifically to post metal pattern, dielectric etch, photoresist strip and residue removal processing.
Most semiconductor devices utilize several different levels of metallization. With the increasing complexity of devices and the need to reduce the physical size of devices, the number of levels which incorporate metal connections is increasing. In addition, with the desire to increase the speed of the devices while reducing the power consumed by the devices, advanced metallization schemes are being developed. One such scheme involves the use of copper-doped aluminum or copper structures for the bus lines and interconnects. Additionally, interlevel dielectrics with lower dielectric constants than standard silicon dioxide films may be used as the dielectric material situated between metallic structures.
A problem that most semiconductor manufacturers face is the cleaning up of the metallic structures after the structures are patterned and etched. More specifically, the photoresist needs to be removed, and the residual metal halide etch byproducts have to be removed or converted to different chemical forms to avoid corrosion of the metal. These processes, commonly known as photoresist strip and passivation processes, may cause non-conducting residues to form on the metallic structure. In order to address this problem, a cleaning step is typically performed after the metal structure is exposed and the photoresist is removed. The cleanup step will preferably remove all of the residue, typically comprised of inorganic polymers, that are formed on the metal structure, thus inhibiting corrosion of the metal structures. However, the clean step must not appreciably affect the electrical critical dimension (CD) of the metal structure.
Typically, for a metallization scheme consisting primarily of Al, the cleanup process consists of an HF vapor etch and an optional solvent clean. More specifically, an O2/H2O plasma photoresist strip and metal passivation step is performed followed by an ex situ HF vapor etch and solvent cleanup. The use of the separate HF vapor treatment equipment and the subsequent solvent xe2x80x9cwetxe2x80x9d clean increases processing costs and reduces production throughput. The use of a solvent is additionally undesirable due to environmental issues. Solvent recycling further increases the cost of the traditional cleanup process. In addition, both the HF vapor and solvent clean can cause CD loss, and may undercut the TiN/Ti barrier layers between the conductor and the dielectric substrate. Such cleanup processes may not sufficiently passivate the aluminum conductors, thereby resulting in the corrosion of the structure. Hence, a dry process which is environmentally friendly and which passivates the metal structure would be preferable. The use of an O2/H2O plasma passivation and photoresist strip step followed by an in situ O2/CF4 or H2O/CF4 plasma clean step to remove the polymer residue from the metal structure has been used. However, the fluorine plasma may erode the process equipment in which this step is performed (e.g. any quartz parts in the process chamber would be eroded by the fluorine containing plasma).
For a typical Cu metallization scheme, a standard O2 plasma ash is performed to remove photoresist after a via etch process. Ashing with O2 causes substantial oxidation to any exposed Cu at the bottom of the via. Therefore, a Si3N4 barrier layer is typically deposited to prevent Cu oxidation. Dielectric etch and photoresist removal are then completed with no exposed Cu. The nitride barrier layer must then be removed in a separate wet or dry etch process. Thus, a dry plasma etch process which could be used to remove photoresist without oxidation of Cu would simplify the process flow by either eliminating the need for the Si3N4 barrier layer, or substantially thinning it (it might still be useful as an etch stop layer for via formation). Removal or thinning of the Si3N4 barrier layer would ease the oxide etch selectivity requirements since stopping the etch on Si3N4 would not be necessary.
An embodiment of the instant invention is a hydrogen-containing plasma processing step to be used after the metal structure is etched. This novel step will passivate most metal structures, remove the polymeric residue from the sidewalls of the metal structures, and will remove the photoresist. In addition, this novel step has the following advantages over the prior art methods: it is a higher throughput process, it can be done in situ in any resist strip equipment regardless of the plasma energy source (e.g. a downstream microwave plasma source or a conventional RF plasma source), it provides better passivation of the exposed metal pattern by converting the metal halide residues into volatile hydrogen halides, it does not appreciably oxidize the exposed Cu and therefore may be used in structures without Cu barrier layers present, it does not produce hazardous waste, and it does not corrode the processing equipment.
An embodiment of the instant invention is a method of fabricating an electronic device formed on a semiconductor wafer, the method comprising the steps of: forming a layer of a first material over the substrate; forming a photoresist layer over the layer of the first material; patterning the layer of the first material; removing the photoresist layer after patterning the layer of the first material; and subjecting the semiconductor wafer to a plasma which incorporates a gas which includes hydrogen or deuterium so as to remove residue from the first material. Preferably, the step of removing the photoresist layer is performed by subjecting the semiconductor wafer to the plasma which incorporates a gas which substantially includes hydrogen or deuterium. The gas which includes hydrogen or deuterium is, preferably, comprised of a gas selected from the group consisting of: NH3, N2H2, H2S, CH4, and deuterated forms of these gases, and may, additionally, include a forming gas. The forming gas is, preferably, comprised of a gas consisting of: argon, nitrogen, and any other inert gas. The electronic device is, preferably, selected from the group consisting of: a memory device, a DRAM device, a logic device, a processor, a DSP, a microprocessor, and any combination thereof. Preferably, the first material is comprised of a conductive material which is not substantially sensitive to oxygen. More specifically, first material is, preferably, comprised of aluminum. The step of subjecting the semiconductor wafer to the plasma which incorporates the gas which includes hydrogen or deuterium passivates the patterned layer of the first material.
Another embodiment of the instant invention is a method of forming a conductive feature comprised of a material which is not substantially sensitive to oxygen over a semiconductor substrate for an electronic device, the method comprising the steps of: forming a conductive layer over the semiconductor substrate, the conductive layer comprised of the material which is not substantially sensitive to oxygen; forming a photoresist layer over the conductive layer, the photoresist having a pattern so as to expose portions of the conductive layer; removing the exposed portions of the conductive layer so as to form the conductive structure; and subjecting the semiconductor wafer to a plasma which incorporates a gas which includes hydrogen or deuterium to remove photoresist from the material. Preferably, the material which is not substantially sensitive to oxygen is comprised of aluminum, and the gas is comprised of a gas selected from the group consisting of: H2, D2, NH3, N2H2, H2S, CH4, and deuterated forms of these gases. Preferably, any residue formed on exposed portions of the conductive feature are removed during the step of subjecting the semiconductor wafer to a plasma which incorporates a gas which includes hydrogen or deuterium. The step of subjecting the semiconductor wafer to a plasma which incorporates a gas which includes hydrogen or deuterium, preferably, passivates the conductive structure.
Another embodiment of the instant invention is a method of forming an interconnecting conductive structure comprised of a conductive material which is not substantially sensitive to oxygen over a semiconductor substrate, the method comprising the steps of: forming a first conductive structure over the semiconductor substrate; forming a dielectric layer over the substrate and the first conductive structure; forming a photoresist layer over the dielectric layer, the photoresist layer having a pattern so as to expose a portion of the dielectric layer which overlays a portion of the first conductive structure; removing the exposed portion of the dielectric layer so as to form an opening in the dielectric layer which exposes a portion of the first conductive structure; subjecting the exposed portion of the first conductive structure to a plasma which incorporates a gas which includes hydrogen or deuterium so as to remove residue formed on the exposed portion of the first conductive structure; forming a conductive material over the dielectric layer and within the opening in the dielectric layer, the conductive material making an electrical contact with the first conductive structure; and removing portions of the conductive material over the dielectric layer so as to form the interconnecting conductive structure. Preferably, the step of subjecting the exposed portion of the first conductive structure to a plasma which incorporates a gas which includes hydrogen or deuterium removes the photoresist layer, and/or it passivates the exposed portion of the first conductive structure. The interconnecting conductive structure is, preferably, comprised of aluminum, and the first conductive structure is comprised of material which is substantially the same as the interconnecting conductive structure. The gas is, preferably, comprised of a gas selected from the group consisting of: H2, D2, NH3, N2H2, H2S, CH4, and deuterated forms of these gases.